Systems and methods for dynamic scanning with multi-head camera

ABSTRACT

A nuclear medicine (NM) multi-head imaging system is provided that includes a gantry, plural detector units mounted to the gantry, and at least one processor operably coupled to at least one of the detector units. The detector units are mounted to the gantry. Each detector unit defines a detector unit position and corresponding view oriented toward a center of the bore. Each detector unit is configured to acquire imaging information over a sweep range corresponding to the corresponding view. The at least one processor is configured to, for each detector unit, determine plural angular positions along the sweep range corresponding to boundaries of the object to be imaged, generate a representation of each angular position for each detector unit position, generate a model based on the angular positions using the representation, and determine scan parameters to be used to image the object using the model.

RELATED APPLICATIONS

The present application claims priority to and is a continuation of U.S.patent application Ser. No. 15/282,521, entitled “Systems and Methodsfor Dynamic Scanning with Multi-Head Camera,” filed Sep. 30, 2016, whichis a continuation-in-part of U.S. patent application Ser. No.14/788,180, filed Jun. 30, 2015, which has issued as U.S. Pat. No.10,143,437, entitled “Systems and Methods for Dynamic Scanning withMulti-Head Camera.” The entire disclosures of U.S. patent applicationSer. No. 15/282,521 and U.S. patent application Ser. No. 14/788,180 areincorporated herein by reference.

BACKGROUND

The subject matter disclosed herein relates generally to medical imagingsystems, and more particularly to radiation detection systems.

In nuclear medicine (NM) imaging, such as single photon emissioncomputed tomography (SPECT) or positron emission tomography (PET)imaging, radiopharmaceuticals are administered internally to a patient.Detectors (e.g., gamma cameras), typically installed on a gantry,capture the radiation emitted by the radiopharmaceuticals and thisinformation is used, by a computer, to form images. The NM imagesprimarily show physiological function of, for example, the patient or aportion of the patient being imaged.

An NM imaging system may be configured as a multi-head imaging systemhaving a number of individual detectors distributed about the gantry.Each detector may pivot or sweep to provide a range over which thedetector may acquire information that is larger than a stationary fieldof view of the detector. However, as a detector sweeps through a range,the detector may acquire imaging information that is not of interest, ornot as useful as information from a region of interest that is coveredby only a portion of a range. The time spent by the detector collectinginformation that is not of interest may result in an inefficientacquisition time.

BRIEF DESCRIPTION

In accordance with an embodiment, a nuclear medicine (NM) multi-headimaging system is provided that includes a gantry, plural detector unitsmounted to the gantry, and at least one processor operably coupled to atleast one of the detector units. The gantry defines a bore configured toaccept an object to be imaged. The detector units are mounted to thegantry, with each detector unit defining a detector unit position andcorresponding view oriented toward a center of the bore. Each detectorunit is configured to acquire imaging information over a sweep rangecorresponding to the corresponding view. The at least one processor isconfigured to, for each detector unit, determine plural angularpositions along the sweep range corresponding to boundaries of theobject to be imaged, generate a representation of each angular positionfor each detector unit position (e.g., a plot for each angular positionfor each detector unit position), generate a model based on the angularpositions using the representation (e.g., generate an angular positionalcurve for each angular position using the plot), and determine scanparameters to be used to image the object using the model (e.g., usingthe angular positional curves).

In accordance with another embodiment, a method includes determining,for each detector unit of an imaging system distributed about a bore ofa gantry, plural angular positions along a corresponding sweep range.The method also includes generating a representation of each angularposition for each detector unit position (e.g., a plot for each angularposition for each detector unit position), and generating a model basedon the angular positions using the representation (e.g., generate anangular positional curve for each angular position using the plot).Also, the method includes determining scan parameters to be used toimage the object using the model (e.g., using the angular positionalcurves). Further, the method includes acquiring imaging informationusing the determined scan parameters. The method also includesreconstructing an image using the imaging information.

In accordance with another embodiment, a method includes determining aregularly shaped footprint that surrounds an irregular shape of anobject to be imaged. The method also includes advancing at least some ofa group of detector units distributed about a bore of a gantry to theregularly shaped footprint. Further, the method includes acquiringimaging information with the at least some of the detector unitspositioned at the regularly shaped footprint.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic view of a nuclear medicine (NM) imagingsystem according to an embodiment.

FIG. 2 provides a schematic view of a detector arrangement according toan embodiment.

FIG. 3 depicts sweep and acquisition ranges for a detector unitaccording to an embodiment.

FIG. 4 illustrates an example scenario of control of the sweep of adetector unit in accordance with an embodiment.

FIG. 5 provides a schematic view of a detector head in accordance withan embodiment.

FIG. 6 shows a sectional view of the detector head of FIG. 5 .

FIG. 7 shows a flowchart of a method, according to an embodiment.

FIG. 8 shows a schematic view of an imaging system, according to anembodiment.

FIG. 9 depicts detector unit positions in accordance with variousembodiments.

FIG. 10 depicts an example detector unit sweep range in accordance withvarious embodiments.

FIG. 11 depicts example angular position curves in accordance withvarious embodiments.

FIG. 12 a depicts an example irregularly shaped footprint resulting froman irregularly shaped object.

FIG. 12 b depicts a regularly shaped footprint in accordance withvarious embodiments.

FIG. 13 shows a flowchart of a method, according to an embodiment.

FIG. 14 a depicts an imaging system with a first group of detectorsadvanced and a second group of detectors retracted, according to anembodiment.

FIG. 14 b depicts the imaging system of FIG. 14 a with the second groupof detectors advanced and the first group of detectors retracted.

FIG. 15 shows a flowchart of a method, according to an embodiment.

FIG. 16 depicts an imaging system in accordance with variousembodiments.

FIG. 17 shows a flowchart of a method, according to an embodiment.

FIG. 18 provides a schematic view of an imaging system in accordancewith various embodiments.

DETAILED DESCRIPTION

The foregoing summary, as well as the following detailed description ofcertain embodiments and claims, will be better understood when read inconjunction with the appended drawings. To the extent that the figuresillustrate diagrams of the functional blocks of various embodiments, thefunctional blocks are not necessarily indicative of the division betweenhardware circuitry. Thus, for example, one or more of the functionalblocks (e.g., processors, controllers or memories) may be implemented ina single piece of hardware (e.g., a general purpose signal processor orrandom access memory, hard disk, or the like) or multiple pieces ofhardware. Similarly, the programs may be stand alone programs, may beincorporated as subroutines in an operating system, may be functions inan installed software package, and the like. It should be understoodthat the various embodiments are not limited to the arrangements andinstrumentality shown in the drawings.

As used herein, the terms “system,” “unit,” or “module” may include ahardware and/or software system that operates to perform one or morefunctions. For example, a module, unit, or system may include a computerprocessor, controller, or other logic-based device that performsoperations based on instructions stored on a tangible and non-transitorycomputer readable storage medium, such as a computer memory.Alternatively, a module, unit, or system may include a hard-wired devicethat performs operations based on hard-wired logic of the device.Various modules or units shown in the attached figures may represent thehardware that operates based on software or hardwired instructions, thesoftware that directs hardware to perform the operations, or acombination thereof.

“Systems,” “units,” or “modules” may include or represent hardware andassociated instructions (e.g., software stored on a tangible andnon-transitory computer readable storage medium, such as a computer harddrive, ROM, RAM, or the like) that perform one or more operationsdescribed herein. The hardware may include electronic circuits thatinclude and/or are connected to one or more logic-based devices, such asmicroprocessors, processors, controllers, or the like. These devices maybe off-the-shelf devices that are appropriately programmed or instructedto perform operations described herein from the instructions describedabove. Additionally or alternatively, one or more of these devices maybe hard-wired with logic circuits to perform these operations.

As used herein, an element or step recited in the singular and precededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” are not intended to beinterpreted as excluding the existence of additional embodiments thatalso incorporate the recited features. Moreover, unless explicitlystated to the contrary, embodiments “comprising” or “having” an elementor a plurality of elements having a particular property may includeadditional such elements not having that property.

Various embodiments provide systems and methods for reducing acquisitiontime and/or improving image quality for NM imaging systems including atleast one detector that sweeps over a range during image acquisition.

For example, in some embodiments, detectors of a multi-head camera beginscanning a patient with the heads of the detectors at an extreme viewangle (e.g., at an edge or boundary of a sweep range). It may be notedthat in other embodiments the detector heads may begin at otherpositions, which may be different for each detector head. During thefirst cycle or sweep of the detectors over a range, a processorreceiving information (e.g., photon counts) from the detectors monitorsthe received information. When the activity (e.g., photon counts)corresponding to a region of interest of the patient comes into view ofa sweeping detector, the processor dynamically marks the view angle as astart of an acquisition range. The heads continue to pivot and theprocessor continues to monitor collected information. When the activitycomes out of view, the processor dynamically marks the correspondingview angle as the end of the acquisition range. The pivot direction maythen be reversed and the head scans from the end of the acquisitionrange to the start of the range. In some embodiments, the pivotdirection may be reversed again and the head scans from the start of therange to the end of the range. The process may repeat a number of timesuntil a desired amount of imaging information has been collected.

In some embodiments, a user may input at least one numerical patientparameter, such as one or more of weight, head radius, headcircumference, body mass index, or the like. Additionally oralternatively, at least one numerical patient parameter may be accessedfrom a patient file. A processor of the imaging system may thencalculate a patient adapted initial starting point for the scan based onthe one or more numerical patient parameters.

A technical effect of at least one embodiment includes improved imagequality. A technical effect of at least one embodiment includes reducedacquisition time.

FIG. 1 provides a schematic view of a nuclear medicine (NM) multi-headimaging system 100 in accordance with various embodiments. Generally,the imaging system 100 is configured to acquire imaging information(e.g., photon counts) from an object to be imaged (e.g., a humanpatient) that has been administered a radiopharmaceutical. The depictedimaging system 100 includes a gantry 110 and a processing unit 120.

The gantry 100 defines a bore 112. The bore 112 is configured to acceptan object to be imaged (e.g., a human patient or portion thereof). Asseen in FIG. 1 , plural detector units 115 are mounted to the gantry110. In the illustrated embodiment, each detector unit 115 includes anarm 114 and a head 116. The arm 114 is configured to articulate the head116 radially toward and/or away from a center of the bore 112 (and/or inother directions), and the head 116 includes at least one detector, withthe head 116 disposed at a radially inward end of the arm 114 andconfigured to pivot to provide a range of positions from which imaginginformation is acquired.

The detector of the head 116, for example, may be a semiconductordetector. For example, a semiconductor detector various embodiments maybe constructed using different materials, such as semiconductormaterials, including Cadmium Zinc Telluride (CdZnTe), often referred toas CZT, Cadmium Telluride (CdTe), and Silicon (Si), among others. Thedetector may be configured for use with, for example, nuclear medicine(NM) imaging systems, positron emission tomography (PET) imagingsystems, and/or single photon emission computed tomography (SPECT)imaging systems.

In various embodiments, the detector may include an array of pixelatedanodes, and may generate different signals depending on the location ofwhere a photon is absorbed in the volume of the detector under a surfaceif the detector. The volumes of the detector under the pixelated anodesare defined as voxels (not shown). For each pixelated anode, thedetector has a corresponding voxel. The absorption of photons by certainvoxels corresponding to particular pixelated anodes results in chargesgenerated that may be counted. The counts may be correlated toparticular locations and used to reconstruct an image.

In various embodiments, each detector unit 115 may define acorresponding view that is oriented toward the center of the bore 112.Each detector unit 115 in the illustrated embodiment is configured toacquire imaging information over a sweep range corresponding to the viewof the given detector unit. FIG. 2 illustrates a detector arrangement200 in accordance with various embodiments. The detector units of FIG. 1, for example, may be arranged in accordance with aspects of thedetector arrangement 200. In some embodiments, the system 100 furtherincludes a CT (computed tomography) detection unit 140. The CT detectionunit 140 may be centered about the bore 112. Images acquired using bothNM and CT by the system are accordingly naturally registered by the factthat the NM and CT detection units are positioned relative to each otherin a known relationship. A patient may be imaged using both CT and NMmodalities at the same imaging session, while remaining on the same bed,which may transport the patient along the common NM-CT bore 112.

As seen in FIG. 2 , the detector arrangement 200 includes detector units210(a), 210(b), 210(c), 210(d), 210(e), 210(f), 210(g), 210(h), 210(i),210(j), 210(k), 210(l) disposed about and oriented toward (e.g., adetection or acquisition surface of the detector units, and/or thecollimator's FOV (Field Of View), are oriented toward) an object 202 tobe imaged in the center of a bore. Each detector unit of the illustratedembodiment defines a corresponding view that may be oriented toward thecenter of the bore of the detector arrangement 200. The view for eachdetector unit 210, for example, may be aligned along a central axis of acorresponding arm (e.g., arm 114) of the detector unit 210. In theillustrated embodiment, the detector unit 210(A) defines a correspondingview 220(A), the detector unit 210(B) defines a corresponding view220(B), the detector unit 210(C) defines a corresponding view 220(C),and so on. The detector units 210 are configured to sweep or pivot (thussweeping the corresponding FOV's) over a sweep range (or portionthereof) bounded on either side of a line defined by the correspondingview during acquisition of imaging information. Thus, each detector unit210 may collect information over a range larger than a field of viewdefined by a stationary detector unit. It may be noted that, generally,the sweeping range that a detector may pivot may be larger than thecorresponding view during acquisition. In some cameras, the sweepingrange that a detector may pivot may be unlimited (e.g., the detector maypivot a full 360 degrees), while in some embodiments the sweeping rangeof a detector may be constrained, for example over 180 degrees (from a−90 degree position to a +90 degree position relative to a positionoriented toward the center of the bore).

With continued reference to FIG. 1 , the depicted processing unit 120 isconfigured to dynamically determine, during a primary image acquisition,at least one boundary of an acquisition range corresponding to an uptakevalue of an object to be imaged for at least one of the detector units115. The acquisition range is smaller than the sweep range, or maximumrange of coverage, of the at least one detector unit 115. A primaryimage acquisition, as used herein, may be understood as a scanningprocedure or process used to collect imaging information forreconstruction of an image. The primary image acquisition may, forexample, be performed over a specified time period or to collect aspecified number of counts corresponding to an amount of informationsufficient to provide a diagnostically useful resolution. For thepurposes of clarity and avoidance of doubt, a scout scan, or other“pre-scan” utilized for the purposes of locating an organ or portionthereof and/or the boundaries of the patient, and/or for positioningimaging equipment but not used or not sufficient for reconstruction ofan image used for diagnostic purposes, are not examples of a primaryimage acquisition. The processing unit 120 is also configured to controlthe at least one detector unit 115 to acquire imaging information overthe acquisition range.

FIG. 3 depicts sweep and acquisition ranges for a detector unit 300according to various embodiments. As seen in FIG. 3 , the detector unit300 includes a detector head 310 disposed at an end of a detector arm308. In FIG. 3 , only one detector unit 300 is depicted for ease andclarity of illustration. It may be noted that the detector unit 300 maybe part of an arrangement of plural detector heads, such as depicted inFIGS. 1 and 2 , and that the general principles discussed in connectionwith the detector unit 300 may be applied to one or more additionaldetector units of a multi-head camera imaging system. In FIG. 3 , thedetector unit 300 may be used to acquire imaging information (e.g.,photon counts) of an object 303 having a region of interest 302. In theillustrated embodiment, the region of interest 302 (or ROI 302) issurrounded by surrounding tissue 322. The region of interest 302, forexample, may be an organ such as the heart or brain (or portionthereof), and may have a substantially larger uptake of an administeredradiopharmaceutical than surrounding tissue 322 of the object 303. Acentral axis 312 of the detector unit 300 passes through a center 304 ofthe region of interest 302 (which is disposed at the center of a bore inthe illustrated embodiment). The central axis 312, for example, maycorrespond to a line along the view corresponding to the detector unit300 when the detector unit 300 is at a midpoint of a range of coverageof the detector unit 300, and/or may be aligned with a central axis ofthe detector arm 308 to which the detector head 310 is attached.

In the illustrated embodiment, the detector unit 300 is depicted asaligned with the central axis 312, and may be rotated, pivoted or sweptover a sweep range 309 between a first limit 313 and a second limit 314.In the illustrated embodiment, the first limit 313 and the second limit314 define a sweep range 309 (or maximum range of coverage) of 180degrees. In other embodiments, the sweep range 309 and/or relativepositions of the first limit 313 and second limit 314 may vary from thedepicted arrangement. It may be noted that the sweep range 309 providesmore coverage than is required to collect imaging information of theregion of interest 302. Thus, if the detector unit 300 is swept over thesweep range 309 during a duration of an imaging acquisition, informationthat may be not be useful for diagnostic purposes (e.g., informationtowards the ends of the sweep range 309 that does not includeinformation from the region of interest 302) may be collected. The timeused to collect the information that is not useful for diagnosticpurposes may be more efficiently spent collecting additional informationfrom the region of interest 302. Accordingly, in the illustratedembodiment, the detector unit 310 may be controlled (e.g., by processingunit 120) to be swept or pivoted over an acquisition range 320 insteadof over the entire sweep range 309 during acquisition of imaginginformation.

As seen in FIG. 3 , the acquisition range 320 generally corresponds toedges of the region of interest 302, and is bounded by a first boundary315 and a second boundary 316. The first boundary 315 is located at anangle α in clockwise direction from the central axis 312 (and, in theillustrated embodiment, from the center 304). The second boundary 316 islocated at an angle β in a counterclockwise direction from the centralaxis 312 (and, in the illustrated embodiment, from the center 304). Thelocations of the first boundary 315 and the second boundary 316 may bedetermined, for example, using uptake information acquired as thedetector 300 sweeps over at least a portion of the sweep range 309. Forexample, when a photon count exceeds a predetermined threshold (orpredetermined rate of change), a boundary of the region of interest 302(for which the uptake is higher than surrounding tissue) may bedetermined or identified. If the photon count is increasing past athreshold, a beginning boundary of the region of interest 302 may bedetermined, and if the photon count is decreasing past a threshold, anending boundary of the region of interest 302 may be determined.

It may be noted the boundaries may not necessarily correspond to acentral axis or portion of a field of view of the detector unit, but maycorrespond to an edge or other portion of the field of view. Further,the acquisition range 320 may be configured in various embodiments toinclude surrounding tissue beyond the region of interest 304 (e.g., toprovide background information and/or a margin of error), and/or to omita portion of the region of interest (e.g., to focus acquisition timeeven more strongly on a central portion of the region of interest thatmay be of particular or emphasized interest). For example, theacquisition range 320 may include an amount of background or surroundingtissue for a first phase of an acquisition period and omit background orsurrounding tissue for a second phase.

FIG. 4 illustrates an example scenario 400 of control of the detectorunit 300 during a primary image acquisition period. The detector unit300 begins the example scenario at an initial position 401. In theillustrated embodiment the initial position 401 corresponds to the firstlimit 313. In some embodiments, the initial position may be locatedbetween the first limit 313 and the first boundary 315 of theacquisition range 320. For example, the initial positon 401 may beestimated based on a patient size and/or type of scan to be performed,with the initial position 410 selected to be located a distance outsideof an expected acquisition range. During an initial portion 402, thedetector unit 300 is swept in a counterclockwise direction from thefirst limit 313 and toward the central axis 312. As the detector unit300 is swept, photon counts acquired by the detector unit 300 may besampled and analyzed. When the photon counts reach a predeterminedthreshold (or a rate of increase of photon counts reaches apredetermined threshold), or the photon counts otherwise satisfy ametric configured to identify an increase in counts corresponding to theregion of interest 302 (or portion thereof) entering a field of view ofthe detector unit, a first boundary of an acquisition range (e.g.,acquisition range 320) may be determined at point 404. At point 404, thedetector unit 300 may be controlled to acquire imaging information ofthe region of interest 302. For example, the detector unit 300 may beswept at a first speed over the initial portion 402 starting from theinitial position 401. However, at 404, where the first boundary of theacquisition range begins, the detector unit 300 may be swept at a secondspeed that is slower than the first speed. Accordingly, relatively lesstime is spent covering the initial portion 402 and relatively more timeis spent collecting imaging information for the region of interest overthe acquisition range. In the illustrated embodiment, the point 404corresponding to the first boundary 315 is depicted as occurring at anangle α1, which may have the same value as a of FIG. 3 .

Next, during portion 406, the detector unit 300 is sweptcounterclockwise at an acquisition speed until the second boundary 316of the acquisition range 320 is reached. The second boundary 316 may bedetermined, for example, based on a decrease in the photon countsatisfying a metric (e.g., threshold) corresponding to the transitionfrom the region of interest 302 (which has a relatively high uptake andrelatively high photon count) to a surrounding portion of the object 303(which has a relatively low uptake and relatively low photon count). Itmay be noted that the particular metrics or thresholds used to identifythe boundaries of the acquisition range 320 may be designed or selectedto provide a margin of error such that the acquisition range 320 coversan amount of surrounding tissue in addition to the region of interest302. At 408, with the second boundary 316 identified and reached, thedetector unit 300 may be reversed in direction and controlled to startrotating clockwise toward the first boundary 315. Thus, the detectorunit may be controlled to reverse direction responsive to a reduction inacquired photon counts.

In some embodiments, the detector unit 300 may be controlled to rotateuntil the already determined first boundary is met, at which point thedetector unit 300 may be again reversed to rotate counterclockwise. Inthe illustrated embodiment, the detector unit 300 may be controlled toupdate at least one of the first boundary 315 or the second boundary 316during an acquisition period. In some embodiments, for example, thefirst and/or second boundaries may be updated during each cycle of anacquisition period. In some embodiments, for example, the first and/orsecond boundaries may be updated at predetermined intervals (e.g., every30 seconds, every minute, every other cycle, or every fifth cycle, amongothers). In the illustrated embodiment, during portion 410 of theexample scenario, the photon counts may be collected and analyzed as thedetector unit 300 rotates or sweeps toward the first boundary 315. Inthe illustrated embodiment, a metric corresponding to a decrease inphoton count associated with a boundary of the region of interest 302 isencountered at point 412, or with the detector unit 300 rotated at anangle α2 from the central axis 312. As seen in FIG. 4 , α2 differs fromal, and the first boundary accordingly may be updated to reflect achange in the uptake of the region of interest 302 over time, and/or achange in position of the region of interest 302. Accordingly, during animaging acquisition, one or more boundaries may be updated to furtherfocus time spent during an acquisition on portions of an object forwhich an increased level of uptake is present for improved imagequality, while reducing time spent on portions of the object that arenot of interest.

In the illustrated embodiment, the detector head reverses direction at412 and rotates during portion 414 until the second boundary is reached(or updated) at 415. As seen in FIG. 4 , after point 415, the detectorhead is rotated past the second boundary and then back toward the secondboundary (e.g., at a faster speed than used during portion 414). Theacquisition during portion 416 may be understood as occurring for asupplemental acquisition zone, and may be utilized to collect backgroundinformation and/or provide a margin of error or buffer zone at the endof the acquisition range. While one supplemental acquisition zone forthe second boundary is shown in the illustrated embodiment, it may benoted that a supplemental acquisition zone may be utilized in connectionwith the first boundary as well. Supplemental acquisition zones invarious embodiments may be utilized, for example, during each back andforth sweeping cycle of a detector head, or as another example, atpredetermined intervals (e.g., every 30 seconds, every minute, everyother cycle, or every fifth cycle, among others). At point 417, thesecond boundary is again reached and the detector is swept toward thefirst boundary at an acquisition speed. The acquisition speed isdepicted in the illustrated embodiment as occurring as a number of stepsof predetermined duration. The detector head may be swept back and forthbetween the first and second boundaries during all or a portion of anacquisition period. For example, in some embodiments, the detector headmay be swept over the sweep range or maximum range (or other rangelarger than the acquisition range) to collect background informationover a portion of an acquisition period.

It may be noted that the control of the sweep of the detector unit 300may be performed using only imaging information from the particular viewcorresponding to the detector unit 300, and using only imaginginformation collected by the particular detector unit 300. Informationfrom other views or other detectors may not be utilized in variousembodiments, and the use of pre-scans or associated calculations may beeliminated or reduced. It may be noted that each detector unit may havea dedicated processor (e.g., located on-board the detector unit) thatperforms all or a portion of the calculations required to determine thefirst and second boundaries for that particular detector unit.

As indicated herein, two or more of the detector units (e.g., 310(a),310(b), 310(c) . . . ) may each be controlled using imaging informationacquired by the particular detector unit (e.g., using a control schemeutilizing one or more aspects of example scenario 400). Thus, in variousembodiments, the processing unit 120 (which may include individualprocessors disposed on-board the detectors) may independently determinecorresponding acquisition ranges for at least two of the detector units210, and independently control the at least two of the detector unitsover the corresponding acquisition ranges. For example, in someembodiments, all of the detector units 210 may be independentlycontrolled to acquire imaging information over a particular acquisitionrange unique to a given detector unit using imaging information onlyfrom that given detector unit.

In alternate embodiments, only some of the detector units may becontrolled in accordance with a control scheme incorporating at leastsome aspects of the the example scenario 400 (e.g., determination ofboundaries of an acquisition range using dynamically acquired imaginginformation and control of the detector unit over the determinedacquisition range), while at least one additional detector unit may becontrolled to acquire imaging information over a range that is largerthan an acquisition range determined based on uptake values associatedonly with a given detector unit. As one example, detector units 210(a),210(c), 210(e), 210(g), 220(i), 220(k) may be controlled as disclosedherein, whereas detector units 210(b), 210(d), 210(f), 210(h), 210(j),210(l) may be controlled to collect information over an entire sweeprange or other range.

For example, as seen in FIG. 3 , some detector units may be controlledto acquire information over a corresponding acquisition range 320 asdiscussed herein, while others are controlled to acquire informationover a larger range 311. Thus, for example, multiple structures ofinterest having different uptake rates may be analyzed, with one or moredetectors collecting information for a particular region of interest(e.g., region of interest 302), and one or more other detectorscollecting information for a different and/or larger region of theobject 303.

In some embodiments, the larger range 311 may coincide with the sweeprange 309 or maximum available range of a detector unit. In otherembodiments, the larger range 311 may be predetermined based onestimates and/or measurements of the object 303 or portions thereof. Insome embodiments, the larger range 311 may be determined using a controlscheme incorporating one or more aspects of the example scenario 400,but using different (e.g., lower) thresholds or metrics than used todetermine the acquisition range 320.

Returning to FIG. 1 , the processing unit 120 is operably coupled to thedetector units 115, and acquires imaging information from at least onedetector head 115, and determines boundaries of an acquisition range forthe at least one detector unit 115, for example, based on photon countsencountered during a sweep or pivoting of the detector unit 115.

In various embodiments the processing unit 120 includes processingcircuitry configured to perform one or more tasks, functions, or stepsdiscussed herein. It may be noted that “processing unit” as used hereinis not intended to necessarily be limited to a single processor orcomputer. For example, the processing unit 120 may include multipleprocessors, FPGA's, ASIC's and/or computers, which may be integrated ina common housing or unit, or which may distributed among various unitsor housings (e.g., one or more aspects of the processing unit 120 may bedisposed onboard one or more detector units, and one or more aspects ofthe processing unit 120 may be disposed in a separate physical unit orhousing). The processing unit 120 may perform various operations inaddition to the determination of acquisition range boundaries andcontrol of detector heads. For example, the processing unit 120 mayreconstruct an image using information acquired during primary imageacquisition via the detector units 115. It may be noted that operationsperformed by the processing unit 120 (e.g., operations corresponding toprocess flows or methods discussed herein, or aspects thereof) may besufficiently complex that the operations may not be performed by a humanbeing within a reasonable time period. For example, analyzing photoncounts to identify boundaries of an acquisition range, providing controlsignals to detector units, or the like may rely on or utilizecomputations that may not be completed by a person within a reasonabletime period.

In the illustrated embodiment, the processing unit 120 includes adetermination module 122, a control module 124, and a memory 130. It maybe noted that other types, numbers, or combinations of modules may beemployed in alternate embodiments, and/or various aspects of modulesdescribed herein may be utilized in connection with different modulesadditionally or alternatively. Generally, the various aspects of theprocessing unit 120 act individually or cooperatively with other aspectsto perform one or more aspects of the methods, steps, or processesdiscussed herein.

In the illustrated embodiment, the depicted determination module 122 isconfigured to, responsive to received photon counts, identify boundariesof an acquisition range as disclosed herein. It may be noted that, invarious embodiments, aspects of the determination module 122 may bedistributed among detector units 115. For example, each detector unitmay have a dedicated determination module disposed in the head 116 ofthe detector unit 115. It may be noted that in various embodiments thedetermination of boundaries of an acquisition range of a given detectorunit is determined using imaging information only from the givendetector unit, or without using imaging information from any otherdetector unit.

The depicted control module 124 is configured to, responsive toboundaries determined by the determination module, control one or moredetector heads 116 to sweep over a corresponding acquisition range. Forexample, responsive to an increased photon count (e.g., a photon countsatisfying a predetermined metric corresponding to reaching orapproaching the beginning of a range covering a region of interest), thecontrol module 124 may control a detector head to continue sweeping inan initial direction, but at a slower speed than an initial speedutilized before the increased photon count. As another example,responsive to a decreased photon count (e.g., a photon count satisfyinga predetermined metric corresponding to reaching or approaching the endof a range covering a region of interest), the control module 124 maycontrol a detector head to reverse direction of sweep. It may be notedthat, in various embodiments, aspects of the control module 124 may bedistributed among detector units 115. For example, each detector unitmay have a dedicated control module disposed in the head 116 of thedetector unit 115.

The memory 130 may include one or more computer readable storage media.The memory 130, for example, may store information describing previouslydetermined boundaries of acquisition ranges, predetermined thresholds orother metrics utilized for determining boundaries of acquisition ranges,parameters to be utilized during performance of a scan (e.g., speed ofrotation for acquisition range, speed of rotation for supplement zone,time or total count value over which an acquisition is to be performed),or the like. Further, the process flows and/or flowcharts discussedherein (or aspects thereof) may represent one or more sets ofinstructions that are stored in the memory 130 for direction ofoperations of the imaging system 100.

It may be noted that while the processing unit 120 is depictedschematically in FIG. 1 as separate from the detector units 115, invarious embodiments, one or more aspects of the processing unit 120 maybe shared with the detector units 115, associated with the detectorunits 115, and/or disposed onboard the detector units 115. For example,in some embodiments, at least a portion of the processing unit 120 isintegrated with at least one of the detector units 115. In variousembodiments, at least a portion of the processing unit 120 includes atleast one application specific integrated circuit (ASIC) or fieldprogrammable gate array (FPGA) that is disposed onboard or integratedwith at least one of the detector units.

FIG. 5 is a schematic view of an example detector head 500 formed inaccordance with various embodiments, and FIG. 6 is a sectional view ofthe detector head 500. As seen in FIG. 5 , the detector head 500includes a stepper motor 502 that may be utilized to pivot a detectorcolumn 504. It may be noted that motors other than stepper motors may beused in various embodiments. It may also be noted that the stepsdepicted in FIG. 4 , for example, do not necessarily correspond to theelemental steps of the stepper motor 502. It may further be noted thatcontinuous motion (e.g., of varying speeds) may be utilized inembodiments of the invention, instead of the staircase type motiondepicted in FIG. 4 . Generally, “step and shoot” motion may be employedin various embodiments. In step and shoot motion, the detector israpidly pivoted, and then remains stationary during data collection.Step and shoot motion may be utilized in various embodiments toeliminate or reduce power transients and/or other electronic noiseassociated with activation of electrical motors. Use of step and shootmotion may also be utilized to eliminate orientation uncertaintiesassociated with each collected photon. However, it may be noted that, invarious embodiments, with fine orientation encoders, and frequentsampling of the orientation encoders, detector aiming may be associatedwith each detected photon to sufficient accuracy even if the detectorsare continuously pivoting during data acquisition. The detector column504, for example, may include a shield, a processing board, a detector(e.g., a CZT detector) and a collimator. The detector head 500 alsoincludes a gear 506 coupling the stepper motor to the column 504, aswell as a slip ring 507 (configured to allow for transfer of signalsbetween the rotating detector column 504 and non-rotating components)and a multiplex board 508. In the illustrated embodiment, the detectorhead 500 also includes an air channel 510 configured to provide coolingto components of the detector head 500. As seen in FIG. 6 , the detectorcolumn 504 includes a heat sink 520, a printed circuit board 522 (whichmay incorporate one or more aspects of the processing unit 120), a leadshielding 524, a CZT detector module 526, and collimator 528 that isregistered to the CZT detector module 526 in the illustrated embodiment.Additional details and discussion regarding detector heads is providedin U.S. patent application Ser. No. 14/671,039, entitled “ReducedAirborne Contamination Detector Heads,” filed Mar. 27, 2015, the subjectmatter of which is hereby incorporated by reference in its entirety.

FIG. 7 provides a flowchart of a method 700 for controlling detectorheads of a multi-head imaging system in accordance with variousembodiments. The method 700 (or aspects thereof), for example, mayemploy or be performed by structures or aspects of various embodiments(e.g., systems and/or methods and/or process flows) discussed herein. Invarious embodiments, certain steps may be omitted or added, certainsteps may be combined, certain steps may be performed concurrently,certain steps may be split into multiple steps, certain steps may beperformed in a different order, or certain steps or series of steps maybe re-performed in an iterative fashion. In various embodiments,portions, aspects, and/or variations of the method 700 may be able to beused as one or more algorithms to direct hardware (e.g., one or moreaspects of the processing unit 120) to perform one or more operationsdescribed herein.

At 702, imaging information is acquired. For example, in variousembodiments, imaging information may be acquired as a primary imagingacquisition that will be used to reconstruct an image to be used fordiagnostic purposes. The imaging information for the depicted embodimentis acquired with plural detector units mounted to a gantry defining abore configured to accept an object to be imaged. As discussed herein,each detector unit defines a corresponding view oriented toward a centerof the bore, with each detector unit configured to acquire the imaginginformation over a sweep range corresponding to the view of the givendetector unit.

At 704, as part of the acquisition of imaging information in theillustrated embodiment, at least one of the detector units may begin asweep from an initial point toward a region of interest. The initialpoint in some embodiments may be at a limit of a maximum sweep range ofthe detector unit. In other embodiments, the initial point may bedetermined based on a priori knowledge, such as a size of a patientand/or a type of scan being performed. The detector unit may be swept ata relatively high speed as it is swept from the initial point toward theregion of interest.

At 706, a first boundary of an acquisition range for at least one of thedetector units is determined. The acquisition range is smaller than thesweep range, thereby focusing additional acquisition time on the regionof interest, improving image quality and/or reducing an overall or totalacquisition time. The first boundary, for example, may correspond to atransition within the field of view of the rotating detector unit fromtissue surrounding a region of interest to at least a portion of theregion of interest itself being disposed within the field of view. Forexample, the first boundary may correspond to a position at whichone-half (or other fraction) of the region of interest is within thefield of view of the detector unit. As another example, the firstboundary may be defined when the edge of the ROI is nearing the end ofthe FOV, while at least a substantial part of the FOV is viewing theROI. In various embodiments, a substantial part of the FOV may beunderstood as, for example, over 50% of the area defined by the FOV,over 75% of the area defined by the FOV, or over 90% of the area definedby the FOV, as examples. For example, as seen in FIG. 3 , an FOV 321taken at the first boundary 315 corresponds to an image view 323 shownin FIG. 3 . In the image view 323, an edge 324 between the ROI 302 andsurrounding tissue 322 is located near an edge of the image view 323 orFOV 321. In the depicted embodiment, the first boundary is dynamicallydetermined during the primary image acquisition. The first boundarycorresponds to, and may be determined based on, an uptake value of theobject to be imaged. For example, the uptake value associated with thefirst boundary is larger than the uptake value for tissue surroundingthe region of interest. The first boundary in various embodiments isdetermined based on a change of photon counts acquired by the detectorunit. For example, the first boundary may be determined when the photoncounts acquired by the detector unit increase to a level satisfying apredetermined threshold or metric.

At 708, responsive to the determination and identification of the firstboundary, the speed of the sweeping or pivoting of the detector unit isreduced from an initial speed to an acquisition speed, with the detectorunit still sweeping in the same direction.

At 710, as the detector unit continues to sweep in the initialdirection, a second boundary of the acquisition range is determined. Thesecond boundary, for example, may correspond to a transition within thefield of view of the rotating detector unit from the region of interestitself (or a portion thereof) being disposed within the field of view totissue surrounding the region of interest being disposed within thefield of view. For example, the second boundary may correspond to aposition at which one-half (or other fraction) of the region of interestis within the field of view of the detector unit. In the depictedembodiment, the second boundary is dynamically determined during theprimary image acquisition. The second boundary corresponds to, and maybe determined based on, an uptake value of the object to be imaged. Thesecond boundary in various embodiments is determined based on a changeof photon counts acquired by the detector unit. For example, the secondboundary may be determined when the photon counts acquired by thedetector unit decrease to a level satisfying a predetermined thresholdor metric.

At 712, responsive to the determination and identification of the secondboundary, the direction of the sweeping or pivoting of the detector unitis reversed, with the detector unit swept toward the first boundary.This is schematically depicted in FIG. 7 by the optional steps 708′(sweeping at reduced speed toward the first boundary), 706′ (determiningthe first boundary), and 712′ (again reversing the sweeping directionuntil the second boundary is determined or reached at 710). It may benoted that in some embodiments, at 706′, the previously determined firstboundary may be utilized as a point at which the sweeping is reversed.

It may be noted that the detector unit may be swept back and forthbetween the first and second boundaries until an acquisition period iscompleted. The acquisition period may have a duration corresponding toan amount of time or a number of photon counts sufficient to provide adesired resolution or image quality. As discussed herein, the first andsecond boundaries may be updated during the image acquisition in variousembodiments. It may further be noted that multiple detectors may beindependently controlled, for example using one or more aspects of steps704-712. Further, in some embodiments, one or more detectors may becontrolled pursuant to steps 704-712, while one or more other detectorsare controlled pursuant to a different control scheme, as indicated at714. It should be noted that acquiring imaging information 702 may beconcurrent to steps 704-712′. Optionally, when the pivoting and sweepingrepresented by the chain of steps 712′ is completed (or a given numberof iterations of the chain of steps is completed), a gantry (e.g.,gantry 110) may rotate (or shift as gantry 1004 of FIG. 8 is configuredto shift) to move the detector heads slightly, and the chain of steps704-712′ may be repeated while the detector heads are in differentpositions with respect to the patient. For example, the one or moreother detectors may acquire imaging information over a range larger thanan acquisition range corresponding to the region of interest, forexample, to acquire additional background information and/or to acquireinformation of a different or additional region of interest. The one ormore other detectors may be configured to acquire imaging informationcorresponding to one or more additional regions of interest thatcorresponds to uptake of a different radiopharmaceutical than the regionof interest corresponding to the acquisition range of steps 704-712.

At 716, when the primary acquisition duration has been satisfied, animage is reconstructed using imaging information acquired during theprimary acquisition. It may be noted that the imaging information usedto dynamically adjust the sweeping of at least some of the detectorunits is also used to reconstruct the image.

In some embodiments, a detector head (or detector heads) may start theimaging data acquisition with an FOV of one or more heads pointingdirectly to the center of the bore, or to another position at which theFOV is entirely viewing the ROI. When aimed at the center of the bore,the ROI is within the FOV, and it is most likely that the narrow FOV isentirely viewing the ROI. The detector head (or heads) may then pivot atreduced speed until the second boundary is encountered and determined.The method may then continue as discussed herein, following steps 712,708′, 706′ 712′, 710 and so on. Alternatively, a detector head (orheads) may begin being pointed at the center of the bore or otherposition at which the FOV is entirely viewing the ROI, and rotate orpivot toward the first boundary.

In some embodiments, it may be beneficial to reconstruct the entireobject 303, with the ROI 302 reconstructed at an enhanced resolutionand/or at an enhanced accuracy. Accordingly, more dwell time may bespent while the FOV is aimed at the ROI, and less dwell time while theFOV is aimed at parts of the object 303 (e.g., surrounding tissue 322)which are outside of the ROI 302. Accordingly, in some embodiments, twoadditional boundaries may be determined: first and second objectboundaries at the two ends of the larger range 311 or other range thatincludes portions of the surrounding tissue 322. Sweeping of a detectorhead may then proceed at a fast or intermediate rate between firstobject boundary and first boundary (e.g., while viewing the surroundingtissue 322), with sweeping of the detector head proceeding at a reducedrate between the first and second boundaries (e.g., while viewing theROI 302), and again at a fast or intermediate rate between the secondobject boundary and the second boundary (e.g., while viewing thesurrounding tissue 322).

In various embodiments, pivoting speed may remain slow, however, for Nsweeps between the first and second boundaries, while there are M sweepsbetween the first object boundary and second object boundary. Thus,while the range between the first and second boundaries corresponding tothe ROI is swept N+M times, the range outside the ROI is swept only Mtimes.

Similarly, the sweeping sequence, in some embodiments may be: from thefirst object boundary to the second boundary, then reverse direction andsweep to the first boundary, then reverse direction and sweep to thesecond object boundary, and then reverse the sequence. In this way, theROI is sampled twice as long as the non-ROI parts of the object.

It may be noted that, usually, the radioisotope concentration in thenon-ROI parts of the object is reduced compared to the radioisotopeconcentration in the ROI parts of the object. However, this may notalways be the case, as voids or parts of the body having less affinity,and/or defects in parts of body, may be the subject of the imaging, andthus included in the ROI. It may be noted that the radioisotopeconcentration in the non-ROI parts of the object may generally be highenough to distinguish the non-ROI parts of the object from regionsoutside the object where no radiation is emitted at all. Thus, thedetermination of the object boundaries is generally possible (e.g., byutilizing a lower threshold for determination of the first and secondobject boundaries compared to the first and second boundariescorresponding to the ROI).

Embodiments described herein may be implemented in medical imagingsystems, such as, for example, SPECT, SPECT-CT, PET and PET-CT. Variousmethods and/or systems (and/or aspects thereof) described herein may beimplemented using a medical imaging system. For example, FIG. 8 is aschematic illustration of a NM imaging system 1000 having a plurality ofimaging detector head assemblies mounted on a gantry (which may bemounted, for example, in rows, in an iris shape, or otherconfigurations, such as a configuration in which the movable detectorcarriers 1016 are aligned radially toward the patient-body 1010). Itshould be noted that the arrangement of FIG. 8 is provided by way ofexample for illustrative purposes, and that other arrangements (e.g.,detector arrangements) may be employed in various embodiments. In theillustrated example, a plurality of imaging detectors 1002 are mountedto a gantry 1004. In the illustrated embodiment, the imaging detectors1002 are configured as two separate detector arrays 1006 and 1008coupled to the gantry 1004 above and below a subject 1010 (e.g., apatient), as viewed in FIG. 8 . The detector arrays 1006 and 1008 may becoupled directly to the gantry 1004, or may be coupled via supportmembers 1012 to the gantry 1004 to allow movement of the entire arrays1006 and/or 1008 relative to the gantry 1004 (e.g., transversetranslating movement in the left or right direction as viewed by arrow Tin FIG. 8 ). Additionally, each of the imaging detectors 1002 includes adetector unit 1014, at least some of which are mounted to a movabledetector carrier 1016 (e.g., a support arm or actuator that may bedriven by a motor to cause movement thereof) that extends from thegantry 1004. In some embodiments, the detector carriers 1016 allowmovement of the detector units 1014 towards and away from the subject1010, such as linearly. Thus, in the illustrated embodiment the detectorarrays 1006 and 1008 are mounted in parallel above and below the subject1010 and allow linear movement of the detector units 1014 in onedirection (indicated by the arrow L), illustrated as perpendicular tothe support member 1012 (that are coupled generally horizontally on thegantry 1004). However, other configurations and orientations arepossible as described herein. It should be noted that the movabledetector carrier 1016 may be any type of support that allows movement ofthe detector units 1014 relative to the support member 1012 and/organtry 1004, which in various embodiments allows the detector units 1014to move linearly towards and away from the support member 1012.

Each of the imaging detectors 1002 in various embodiments is smallerthan a conventional whole body or general purpose imaging detector. Aconventional imaging detector may be large enough to image most or allof a width of a patient's body at one time and may have a diameter or alarger dimension of approximately 50 cm or more. In contrast, each ofthe imaging detectors 1002 may include one or more detector units 1014coupled to a respective detector carrier 1016 and having dimensions of,for example, 4 cm to 20 cm and may be formed of Cadmium Zinc Telluride(CZT) tiles or modules. For example, each of the detector units 1014 maybe 8×8 cm in size and be composed of a plurality of CZT pixelatedmodules (not shown). For example, each module may be 4×4 cm in size andhave 16×16=256 pixels (pixelated anodes). In some embodiments, eachdetector unit 1014 includes a plurality of modules, such as an array of1×7 modules. However, different configurations and array sizes arecontemplated including, for example, detector units 1014 having multiplerows of modules.

It should be understood that the imaging detectors 1002 may be differentsizes and/or shapes with respect to each other, such as square,rectangular, circular or other shape. An actual field of view (FOV) ofeach of the imaging detectors 1002 may be directly proportional to thesize and shape of the respective imaging detector.

The gantry 1004 may be formed with an aperture 1018 (e.g., opening orbore) therethrough as illustrated. A patient table 1020, such as apatient bed, is configured with a support mechanism (not shown) tosupport and carry the subject 1010 in one or more of a plurality ofviewing positions within the aperture 1018 and relative to the imagingdetectors 1002. Alternatively, the gantry 1004 may comprise a pluralityof gantry segments (not shown), each of which may independently move asupport member 1012 or one or more of the imaging detectors 1002.

The gantry 1004 may also be configured in other shapes, such as a “C”,“H” and “L”, for example, and may be rotatable about the subject 1010.For example, the gantry 1004 may be formed as a closed ring or circle,or as an open arc or arch which allows the subject 1010 to be easilyaccessed while imaging and facilitates loading and unloading of thesubject 1010, as well as reducing claustrophobia in some subjects 1010.

Additional imaging detectors (not shown) may be positioned to form rowsof detector arrays or an arc or ring around the subject 1010. Bypositioning multiple imaging detectors 1002 at multiple positions withrespect to the subject 1010, such as along an imaging axis (e.g., headto toe direction of the subject 1010) image data specific for a largerFOV may be acquired more quickly.

Each of the imaging detectors 1002 has a radiation detection face, whichis directed towards the subject 1010 or a region of interest within thesubject.

The collimators 1022 (and detectors) in FIG. 8 are depicted for ease ofillustration as single collimators in each detector head. Optionally,for embodiments employing one or more parallel-hole collimators,multi-bore collimators may be constructed to be registered with pixelsof the detector units 1014, which in one embodiment are CZT detectors.However, other materials may be used. Registered collimation may improvespatial resolution by forcing photons going through one bore to becollected primarily by one pixel. Additionally, registered collimationmay improve sensitivity and energy response of pixelated detectors asdetector area near the edges of a pixel or in-between two adjacentpixels may have reduced sensitivity or decreased energy resolution orother performance degradation. Having collimator septa directly abovethe edges of pixels reduces the chance of a photon impinging at thesedegraded-performance locations, without decreasing the overallprobability of a photon passing through the collimator.

A controller unit 1030 may control the movement and positioning of thepatient table 1020, imaging detectors 1002 (which may be configured asone or more arms), gantry 1004 and/or the collimators 1022 (that movewith the imaging detectors 1002 in various embodiments, being coupledthereto). A range of motion before or during an acquisition, or betweendifferent image acquisitions, is set to maintain the actual FOV of eachof the imaging detectors 1002 directed, for example, towards or “aimedat” a particular area or region of the subject 1010 or along the entiresubject 1010. The motion may be a combined or complex motion in multipledirections simultaneously, concurrently, or sequentially.

The controller unit 1030 may have a gantry motor controller 1032, tablecontroller 1034, detector controller 1036, pivot controller 1038, andcollimator controller 1040. The controllers 1030, 1032, 1034, 1036,1038, 1040 may be automatically commanded by a processing unit 1050,manually controlled by an operator, or a combination thereof. The gantrymotor controller 1032 may move the imaging detectors 1002 with respectto the subject 1010, for example, individually, in segments or subsets,or simultaneously in a fixed relationship to one another. For example,in some embodiments, the gantry controller 1032 may cause the imagingdetectors 1002 and/or support members 1012 to move relative to or rotateabout the subject 1010, which may include motion of less than or up to180 degrees (or more).

The table controller 1034 may move the patient table 1020 to positionthe subject 1010 relative to the imaging detectors 1002. The patienttable 1020 may be moved in up-down directions, in-out directions, andright-left directions, for example. The detector controller 1036 maycontrol movement of each of the imaging detectors 1002 to move togetheras a group or individually. The detector controller 1036 also maycontrol movement of the imaging detectors 1002 in some embodiments tomove closer to and farther from a surface of the subject 1010, such asby controlling translating movement of the detector carriers 1016linearly towards or away from the subject 1010 (e.g., sliding ortelescoping movement). Optionally, the detector controller 1036 maycontrol movement of the detector carriers 1016 to allow movement of thedetector array 1006 or 1008. For example, the detector controller 1036may control lateral movement of the detector carriers 1016 illustratedby the T arrow (and shown as left and right as viewed in FIG. 10 ). Invarious embodiments, the detector controller 1036 may control thedetector carriers 1016 or the support members 1012 to move in differentlateral directions. Detector controller 1036 may control the swivelingmotion of detectors 1002 together with their collimators 1022. In someembodiments, detectors 1002 and collimators 1022 may swivel or rotatearound an axis.

The pivot controller 1038 may control pivoting or rotating movement ofthe detector units 1014 at ends of the detector carriers 1016 and/orpivoting or rotating movement of the detector carrier 1016. For example,one or more of the detector units 1014 or detector carriers 1016 may berotated about at least one axis to view the subject 1010 from aplurality of angular orientations to acquire, for example, 3D image datain a 3D SPECT or 3D imaging mode of operation. The collimator controller1040 may adjust a position of an adjustable collimator, such as acollimator with adjustable strips (or vanes) or adjustable pinhole(s).

It should be noted that motion of one or more imaging detectors 1002 maybe in directions other than strictly axially or radially, and motions inseveral motion directions may be used in various embodiment. Therefore,the term “motion controller” may be used to indicate a collective namefor all motion controllers. It should be noted that the variouscontrollers may be combined, for example, the detector controller 1036and pivot controller 1038 may be combined to provide the differentmovements described herein.

Prior to acquiring an image of the subject 1010 or a portion of thesubject 1010, the imaging detectors 1002, gantry 1004, patient table1020 and/or collimators 1022 may be adjusted, such as to first orinitial imaging positions, as well as subsequent imaging positions. Theimaging detectors 1002 may each be positioned to image a portion of thesubject 1010. Alternatively, for example in a case of a small sizesubject 1010, one or more of the imaging detectors 1002 may not be usedto acquire data, such as the imaging detectors 1002 at ends of thedetector arrays 1006 and 1008, which as illustrated in FIG. 8 are in aretracted position away from the subject 1010. Positioning may beaccomplished manually by the operator and/or automatically, which mayinclude using, for example, image information such as other imagesacquired before the current acquisition, such as by another imagingmodality such as X-ray Computed Tomography (CT), MM, X-Ray, PET orultrasound. In some embodiments, the additional information forpositioning, such as the other images, may be acquired by the samesystem, such as in a hybrid system (e.g., a SPECT/CT system).Additionally, the detector units 1014 may be configured to acquirenon-NM data, such as x-ray CT data. In some embodiments, amulti-modality imaging system may be provided, for example, to allowperforming NM or SPECT imaging, as well as x-ray CT imaging, which mayinclude a dual-modality or gantry design as described in more detailherein.

After the imaging detectors 1002, gantry 1004, patient table 1020,and/or collimators 1022 are positioned, one or more images, such asthree-dimensional (3D) SPECT images are acquired using one or more ofthe imaging detectors 1002, which may include using a combined motionthat reduces or minimizes spacing between detector units 1014. The imagedata acquired by each imaging detector 1002 may be combined andreconstructed into a composite image or 3D images in variousembodiments.

In one embodiment, at least one of detector arrays 1006 and/or 1008,gantry 1004, patient table 1020, and/or collimators 1022 are moved afterbeing initially positioned, which includes individual movement of one ormore of the detector units 1014 (e.g., combined lateral and pivotingmovement) together with the swiveling motion of detectors 1002. Forexample, at least one of detector arrays 1006 and/or 1008 may be movedlaterally while pivoted. Thus, in various embodiments, a plurality ofsmall sized detectors, such as the detector units 1014 may be used for3D imaging, such as when moving or sweeping the detector units 1014 incombination with other movements.

In various embodiments, a data acquisition system (DAS) 1060 receiveselectrical signal data produced by the imaging detectors 1002 andconverts this data into digital signals for subsequent processing.However, in various embodiments, digital signals are generated by theimaging detectors 1002. An image reconstruction device 1062 (which maybe a processing device or computer) and a data storage device 1064 maybe provided in addition to the processing unit 1050. It should be notedthat one or more functions related to one or more of data acquisition,motion control, data processing and image reconstruction may beaccomplished through hardware, software and/or by shared processingresources, which may be located within or near the imaging system 1000,or may be located remotely. Additionally, a user input device 1066 maybe provided to receive user inputs (e.g., control commands), as well asa display 1068 for displaying images. DAS 1060 receives the acquiredimages from detectors 1002 together with the corresponding lateral,vertical, rotational and swiveling coordinates of gantry 1004, supportmembers 1012, detector units 1014, detector carriers 1016, and detectors1002 for accurate reconstruction of an image including 3D images andtheir slices.

In various embodiments, scan parameters may be determined, for example,using imaging information (e.g., photon counts) acquired at thebeginning of a scan without reconstructing any images. For example, withcontinued reference to FIG. 1 , each detector unit 115 may also beunderstood as defining a detector unit position. For example, FIG. 9depicts an example imaging system 900 including detector units 115disposed at 12 positions (906(a)-906(l)) around an object 902 to beimaged. It may be noted that the detector units 115 may be configuredgenerally similarly in various respects to the detector units 115discussed in connection with FIG. 1 . For example, each detector unit115 may include an arm 114 and a head 116 as shown in FIG. 1 . Theobject 902 includes a volume of interest 904. For example, the object902 may be a human patient and the volume of interest 904 may be one ormore organs of the patient that are to be evaluated using a scanperformed with the imaging system 900.

The processing unit 120 in various embodiments is configured todetermine plural angular positions (e.g., positions along a sweep range)for each detector unit 115, with the angular positions corresponding toboundaries of the object 902 to be imaged. As seen in FIG. 9 , a firstangular position 950 (defining a viewing angle of a detector unit)corresponds to a first boundary 960 between air and soft tissue, asecond angular position 952 corresponds to a first boundary 962 betweensoft tissue and the volume of interest 904, a third angular position 954corresponds to a second boundary 964 between the volume of interest 904and soft tissue, and a fourth angular position 956 corresponds to asecond boundary 966 between soft tissue and air. Angular positions foronly the first detector unit position 906(a) are shown in FIG. 9 forpurposes of clarity and ease of illustration; however, it may be notedthat corresponding angular positions and boundaries may be employed forthe remaining detector unit positions 906(b)-(l). The boundaries betweenair and tissue, or between different types of tissue, may be determinedfor example, based on photon counts acquired during one or morepreliminary sweeps of the detector unit 115 across the object 902. Forexample, a first amount of increase (or decrease) in photon counts maybe used to determine a transition between air and soft tissue outside ofthe volume of interest, while a second amount of increase (or decrease)in photon counts may be used to determine a transition between thevolume of interest and soft tissue outside of the volume of interest. Itmay be noted that other detector arrangements may be employed inalternate embodiments. For example, the views used to construct arepresentation such as a plot and generate curves or another model usedto determine scan parameters may be views that are arranged along alength of a patient (e.g., a series of views or slabs used to image avolume of interest such as the spinal cord).

FIG. 10 provides a schematic depiction of the sweep range (e.g.,projection data acquired over the sweep range) for the first detectorposition 906(a). In the depicted example, the detector unit 115positioned at the first detector position 906(a) has a sweep range of−90 degrees to +90 degrees. It may be noted that, while the variousangular positions are shown positioned at the various boundaries, insome embodiments the angular positions may be varied to correspond butnot necessarily align with the boundaries, for example the secondangular position 952 and the third angular position 954 may be selectedto provide a slight offset from a corresponding boundary into the softtissue to provide a safety margin to help ensure that the entire volumeof interest 904 is imaged appropriately.

As seen in FIG. 10 , three sweep range portions are defined with respectto the boundaries and angular positions within the object 902 to beimaged. In the illustrated example, a first sweep range portion 970 isdefined between the first angular position 950 and the second angularposition 952, a second sweep range portion 972 is defined between thesecond angular position 952 and the third angular position 954, and athird sweep range portion 974 is defined between the third angularposition 954 and the fourth angular position 956. The first sweep rangeportion 970 and the third sweep range portion correspond to soft tissueof the object 902, and the second sweep range portion corresponds to thevolume of interest 904. For efficient scanning, a relatively largeramount of information may be acquired for the volume of interest 904than for soft tissue outside of the volume of interest. Accordingly, thedetector unit 115 at the first detector unit position 906(a) may beswept at a relatively higher rate over the first sweep range portion 970(between the first angular position 950 and the second angular position952) and also at the relatively higher rate over the third sweep rangeposition 974 (between the third angular position 954 and the fourthangular position 956). However, to acquire more information over thevolume of interest 904 relative to soft tissue outside of the volume ofinterest 904, the detector unit 115 of the depicted example may be sweptat a relatively lower rate over the second sweep range portion 972 (fromthe second angular position 952 to the third angular position 954). Eachdetector unit 115 of the imaging system 900 may controlled using thesame general principles discussed above in connection with the firstdetector unit position 906(a). Accordingly, in various embodiments, oneor more processors (e.g., processing unit 120) may be configured tosweep each detector unit 115 at a first faster rate between the firstangular position 950 and the second angular position 952, sweep eachdetector unit 115 at a second, slower rate between the second angularposition 952 and the third angular position 954, and sweep each detectorunit 115 at the first rate between the third angular position 954 andthe fourth angular position 956.

With continued reference to FIG. 1 along with FIGS. 9 and 10 , asmentioned above, the processing unit 120 in various embodiments isconfigured to determine plural angular positions (e.g., first angularposition 950, second angular position 952, third angular position 954,fourth angular position 956) for each detector unit 115, with theangular positions corresponding to boundaries (e.g., first boundary 960between air and soft tissue, first boundary 962 between soft tissue ofthe object 902 and the volume of interest 904, second boundary 964between the volume of interest 904 and soft tissue, and fourth boundary964 between soft tissue of the object 902 and air) of the object 902 tobe imaged.

Further, the processing unit 120 may be configured (e.g., programmed) togenerate a representation (e.g., plot) for each angular position foreach detector unit position, and to generate a model based on theangular positions using the representation (e.g., generate an angularpositional curve for each angular position using the plot or otherrepresentation). It may be noted that the plot or representation invarious embodiments need not necessarily be printed or otherwiseprovided in a physical format, but may instead be a digitalrepresentation. Further it may be noted that, while a plot utilizingangular positional curves is discussed herein in connection with certainembodiments, other representations and models other than curves (e.g.,straight and/or discontinuous lines or line segments between estimatedor determined points of a plot or other representation; one or moretables including points corresponding to those discussed in connectionwith various embodiments discussed herein) may be utilized in variousembodiments. FIG. 11 illustrates an example plot 1100 used to generateangular positional curves. In the plot 1100, detector unit position isplotted along the x-axis or horizontal axis, and angular position isplotted along the y-axis or vertical axis. The plot 1100 corresponds tothe examples depicted in FIGS. 9 and 10 . Accordingly, the detector unitpositions are plotted from 906(a) to 906(l), and the angular positionsare plotted between a range of −90 to +90 degrees. Points for eachdetector unit position are plotted for the four angular positions (950,952, 954, 956) corresponding to the boundaries determined for eachparticular detector unit position (point 950(a) for the first angularposition 950 for the first detector unit position 906(a), point 950(b)for the first angular position 950 for the second detector unit position906(b), and so on). To generate a first angular position curve 1150, thepoints 950(a)-(l) corresponding to the first angular position 950 forthe various detector unit positions are used. For example, the firstangular position curve 1150 may be generated by determining a curve thatsmoothly connects the points 950(a)-(l). It may be noted that curvesmoothing may be employed to determine an accurate shape as well as tocorrect for any points that may be anomalies or otherwise inaccurate orinconsistent. Similarly, to generate a second angular position curve1160, the points 952(a)-(l) corresponding to the second angular position952 for the various detector unit positions are used. For example, thesecond angular position curve 1160 may be generated by determining acurve that smoothly connects the points 952(a)-(l). Also, to generate athird angular position curve 1170, the points 954(a)-(l) correspondingto the third angular position 954 for the various detector unitpositions are used. For example, the third angular position curve 1170may be generated by determining a curve that smoothly connects thepoints 954(a)-(l). To generate a fourth angular position curve 1180, thepoints 956(a)-(l) corresponding to the fourth angular position 956 forthe various detector unit positions are used. For example, the fourthangular position curve 1180 may be generated by determining a curve thatsmoothly connects the points 956(a)-(l). It may be noted that otherangular positions/boundaries may be employed in other embodiments. Forexample, in embodiments which feature separate volumes of interest(e.g., imaging two kidneys), an additional range of soft tissue betweenthe volumes of interest may be provided using angular positions andboundaries corresponding to transitions between soft tissue and volumesof interest. As another example, in embodiments which will pass overseparate regions of air (e.g., a scan including arms in a separateposition from the body), additional angular positions and boundaries maybe used for additional transitions between soft tissue and air.

The processing unit 120 may also be configured to determine scanparameters to be used to image the object 902 using the angularpositional curves. For example, default or initial scan parameters maybe used to acquire imaging information in one or more preliminary sweepsof the object 902. The imaging information acquired during the one ormore preliminary sweeps may be used to determine the angular positionsand angular position curves as discussed herein. The angular positioncurves may then be used to determine scanning parameters for theremainder of the scanning process. Further, the angular positions andangular position curves may be updated during a scanning process andused to update the scanning parameters. The scanning parametersdetermined using the angular positional curves are generally settingsused to acquire imaging information. As one example, a sweep range maybe determined. In the depicted embodiment, the sweep range may bedefined from the first angular position 950 to the fourth angularposition 954. For instance, whenever a particular detector unit 115reaches its corresponding first angular position 950 or fourth angularposition 954, the detector unit 115 may reverse direction to sweep backtoward the volume of interest 904. As another example, sweep rates (orspeeds of rotation of a detector head as it sweeps) may be determined.In the depicted embodiment, for example, each particular detector unit115 may be controlled to have a faster sweep rate when it sweeps betweenits corresponding first angular position 950 and second angular position952, and when it sweep between its corresponding third angular position954 and fourth angular position 956. Each particular detector unit 115may be controlled to have a slower sweep rate when it sweeps between itscorresponding second angular position 952 and third angular position954. Other scan parameters that may be determined additionally oralternatively include the number of detector units to be employed,radial position (e.g., how close to or far from center of bore ofgantry) of one or more detector units, gantry rotational position, orsequence of positioning of heads.

The positional curves may be used to determine scan parameters for avariety of benefits and/or using a variety of techniques. For example,if the angular positions determined using photon counts of a givendetector at a particular detector position provides plot points that areat a distance from the angular positional curves, revised angularpositions for the particular detector at the particular detectorposition may be determined to more closely match or align with thepositional curves. Additionally or alternatively, photon counts may beacquired using less than all of the detector units disposed around abore, with a curve generated from information collected by the detectorunits that were used to collect photon counts utilized to estimate ordetermine angular positions for other detector units that were not used.Additionally, or alternatively, in various embodiments, the processingunit 120 may determine scan parameters for at least one additionaldetector unit position (e.g., a detector unit position for which photoncounts have not been acquired) corresponding to a rotation of thegantry. For example, the gantry 110 with the detector units 115 attachedmay be positioned at a first rotational position at which photon countsare acquired and used to general angular positional curves as discussedherein. Then, the gantry 110 may be rotated to a new position. Theangular positional curves may be used, for example, to estimate angularpositions for one or more detectors at the new rotational position ofthe gantry, and the angular positions at the new rotational position maybe used to determine corresponding sweep ranges and/or speeds for thedetectors when the imaging system 900 is used to acquire imaginginformation at the new rotational position.

For instance, in one example scenario, an additional detector unitposition that is interposed between a first unit position of a firstdetector unit and a second detector unit position of a second detectorunit, with the processing unit 120 configured to determine an angularposition for the additional detector unit position. For example, withreference to FIG. 11 , a rotation of the gantry may cause the detectorunit 115 associated with the first detector unit position 906(a) toshift to a new position 1106(a) that is interposed between firstdetector unit position 906(a) and second detector unit position 906(b)of the previous gantry rotational position. Using the generated angularpositional curves, points 1190, 1192, 1194, and 1196 may be estimated ordetermined to provide the angular positions for the new position1106(a), which may in turn be used to determine one or more scanningparameters to be used for a detector in the new position 1106(a) (e.g.,sweep range and/or sweep rate).

In various embodiments, the processing unit 120 may also determine oneor more radial positions for detector heads to be used during scanning.For example, in various embodiments, the processing unit 120 isconfigured to determine a regularly shaped footprint that surrounds anirregular shape of the object 904 to be imaged, to advance at least someof the detector units 115 to the regularly shaped footprint, and toacquire imaging information with the at least some of the detector units115 positioned at the regularly shaped footprint (e.g., with a detectorhead positioned at or near the regularly shaped footprint). FIG. 12 adepicts an example irregularly shaped footprint resulting from anirregularly shaped object, and FIG. 12 b depicts a regularly shapedfootprint in accordance with various embodiments.

As seen in FIG. 12 a , an object 1202 to be imaged has an irregularshape 1204. For example, the object 1202 has various portions thatswitch between convex and concave, as well as portions with rapid ordiscontinuous changes in curvature. In FIG. 12 a , detector units 1210are brought into close proximity with the object 1202; however, thepositioning of the detector units 1210 in close proximity with theirregularly shaped object can affect the available sweep ranges of thedetector units 1210 and/or result in imaging artifacts (e.g., due tomissing information from an unavailable portion of a sweep range). Forexample, an unavailable portion of a sweep range may result from a limit(e.g., −90 to +90 degrees of rotation) of the sweep range, and/or due toan obstruction of part of the object by an adjacent detector. In variousembodiments, to eliminate or reduce such artifacts, the detector units1210, instead of being brought into close proximity, are advanced to aregularly shaped footprint that surrounds the irregular shape 1204. Asseen in FIG. 12 b , the detector units 1210 are advanced to a regularlyshaped footprint 1220 that surrounds the irregular shape 1204 of theobject 1202. In some embodiments, the irregular shape 1204 and regularlyshaped footprint 1220 may share a common border at one or more portionsalong the perimeter of the regularly shaped footprint 1220, while inother embodiments a gap may be present along the entire perimeterbetween the irregular shape 1204 and the regularly shaped footprint1220. A footprint may be understood as being regularly shaped becauseone or more of: the footprint is defined by a single mathematicalrelationship of function, the footprint is smooth and continuous, thefootprint is devoid of switches between convex and concave shapes, orthe footprint is devoid of rapid or discontinuous changes in curvature.In the illustrated embodiments, the regularly shaped footprint 1220 isan ellipsoid (e.g., a non-circular ellipsoid).

FIG. 13 provides a flowchart of a method 1300 for controlling detectorheads of a multi-head imaging system in accordance with variousembodiments. The method 1300 (or aspects thereof), for example, mayemploy or be performed by structures or aspects of various embodiments(e.g., systems and/or methods and/or process flows) discussed herein. Invarious embodiments, certain steps may be omitted or added, certainsteps may be combined, certain steps may be performed concurrently,certain steps may be split into multiple steps, certain steps may beperformed in a different order, or certain steps or series of steps maybe re-performed in an iterative fashion. In various embodiments,portions, aspects, and/or variations of the method 1300 may be able tobe used as one or more algorithms to direct hardware (e.g., one or moreaspects of the processing unit 120) to perform one or more operationsdescribed herein.

At 1302, a regularly shaped footprint is determined for an object to beimaged. For example, the object to be imaged (e.g., object 1204) mayhave an irregular shape that switches between convex and concave atvarious portions. The regularly shaped footprint may have a smooth,continuous, convex shape that surrounds (e.g., completely surrounds) theirregular shape of the object to be imaged. The regularly shapedfootprint, for example, may have the shape of an ellipsoid (e.g., anon-circular ellipsoid).

At 1304, at least some of the detector units of an imaging system areadvanced to the regularly shaped footprint. In some embodiments, all ofthe detector units are advanced to the regularly shaped footprint. Inother embodiments, some of the detector units may be advanced whileothers are left in a retracted position or position distant from theregularly shaped footprint. In some embodiments, a first group ofdetectors may be brought to the regularly shaped footprint and used toacquire imaging information while a second group of detectors isretracted, and, after the acquisition by the first group of detectors,the first group may be retracted and the second group advanced to theregularly shaped footprint, with the second group then used to acquireimaging information while the first group is retracted.

At 1306, imaging information is acquired with at least some of thedetector units positioned at the regularly shaped footprint. In someembodiments, a first group of detectors may be brought to the regularlyshaped footprint and used to acquire imaging information while a secondgroup of detectors is retracted, and, after the acquisition by the firstgroup of detectors, the first group may be retracted and the secondgroup advanced to the regularly shaped footprint, with the second groupthen used to acquire imaging information while the first group isretracted. At 1308, an image is reconstructed using imaging informationacquired at 1306.

Additionally or alternatively, in some embodiments, the processing unit120 is configured to advance or position radially inwardly differentgroups of detectors at different times. FIGS. 14 a and 14 b depict anexample imaging system 1400 with different groups of detectors advancedand retracted. As seen in FIG. 14 a , a first group 1410 of detectorunits 1412 are at a radially inward position 1450, while a second group1420 of detector units 1422 are at a radially outward position 1460.However, in the configuration shown in FIG. 14 b , the first group 1410of detector units 1412 are at the radially outward position 1460, whilethe second group 1420 of detector units 1422 are at the radially inwardposition 1450. In the configuration shown in FIG. 14 a , the first group1410 may be used to acquire imaging information proximate an object tobe imaged, with the second group 1420 out of the way, while in theconfiguration shown in FIG. 14 b , the second group 1420 may be usedacquire imaging information proximate the object with first group 1410out of the way. Accordingly, more detectors from various angles or viewsmay be used proximate to an object than would be possible if only onegroup were positioned proximate to the object. For example, some objectsmay be small enough such that detectors would collide if all wereattempted to be brought proximate to the object.

To achieve positioning such as that shown in FIGS. 14 a and 14 b , aprocessing unit (e.g., processing unit 120) may be configured to advancethe first group 1410 of the detector units 1412 to the radially inwardposition 1450 while leaving the second group 1420 of the detector units1422 at the radially outward position 1460. The processing unit may thencontrol the imaging system 1400 to acquire imaging information with thefirst group 1410 of detector units 1412 at the radially inward position1450. Next, the processing unit may retract the first group 1410 ofdetector units 1412 to the radially outward position 1460, and advancethe second group 1420 of detector units 1422 to the radially inwardposition 1450. With the second group 1420 at the radially inwardposition 1450, additional imaging information may be acquired with thesecond group 1420 of detectors 1422. It may be noted that in someembodiments detectors at the radially outward position 1460 may be usedto acquire imaging information, while in other embodiments, onlydetectors at the radially inward position 1450 may be utilized toacquire imaging information. It may further be noted that two groups ofdetectors are depicted in FIG. 14 for ease and clarity of illustration;however, in other embodiments more than two groups may be used. Forexample, three groups of detectors may be used, with two groupsmaintained at an outward position when the remaining group is at aninward position.

FIG. 15 provides a flowchart of a method 1500 for controlling detectorheads of a multi-head imaging system in accordance with variousembodiments. The method 1500 (or aspects thereof), for example, mayemploy or be performed by structures or aspects of various embodiments(e.g., systems and/or methods and/or process flows) discussed herein. Invarious embodiments, certain steps may be omitted or added, certainsteps may be combined, certain steps may be performed concurrently,certain steps may be split into multiple steps, certain steps may beperformed in a different order, or certain steps or series of steps maybe re-performed in an iterative fashion. In various embodiments,portions, aspects, and/or variations of the method 1500 may be able tobe used as one or more algorithms to direct hardware (e.g., one or moreaspects of the processing unit 120) to perform one or more operationsdescribed herein.

At 1502, an object to be imaged is positioned within the bore of agantry (e.g., gantry 110). Plural detector units are disposed around thecircumference of the bore. The detector units include detector headsthat are articulable radially, such that the detector heads may beadvanced radially toward the object to be imaged or retracted radiallyaway from the object to be imaged.

At 1504, a first group of detector units is advanced to a radiallyinward position. While the first group is advanced, a second group ofdetector units is left at a radially outward position. (See, e.g., FIG.14 a .)

At 1506, imaging information is acquired with the first group ofdetector units at the first radially inward position. In someembodiments, imaging information is also acquired with the second groupof detectors at the radially outward position, while in otherembodiments information no imaging information is acquired with thesecond group of detectors at the radially outward position.

At 1508, the first group of detector units is retracted to the radiallyoutward position, and, at 1510, the second group of detector units isadvanced to the radially inward position. (See, e.g., FIG. 14 b .)

At 1512, imaging information is acquired with the second group ofdetector units at the first radially inward position. In someembodiments, imaging information is also acquired with the first groupof detectors at the radially outward position, while in otherembodiments information no imaging information is acquired with thefirst group of detectors at the radially outward position.

At 1513, it is determined if the acquisition is ended (e.g., no moreimaging information is to be acquired). If the acquisition is not ended,in the depicted embodiment, at 1515, the gantry may be rotated and themethod 1500 return to 1504 for additional positioning of detector unitsand acquisition of imaging information. It may be noted that or moredetector units may be retracted from a previous imaging position beforerotating the gantry.

If the acquisition is ended, the method 1500 proceeds to 1514. At 1514,an image is reconstructed using the information acquired at 1506 and1512.

It may be noted that in various embodiments, differently configureddetector units may be used in conjunction with each other. For example,FIG. 16 provides a schematic view of an imaging system 1600. The imagingsystem 1600 may be generally similar in certain aspects to other imagingsystems discussed herein. As seen in FIG. 16 , the imaging system 1600includes a first group 1610 of primary detector units 1612, and a secondgroup 1620 of supplemental detector units 1622. In the illustratedexample, the primary detector units 1612 and supplemental detector units1622 are positioned alternately about the bore 1602.

The primary detector units 1612 each include an arm 1614 and include arange of motion 1616. The arms 1614 of the primary detector units 1612may be extended or retracted (or otherwise articulated) to move theprimary detector units 1612 radially toward or away from a bore 1602 ofthe imaging system 1600. Similarly, the supplemental detector units 1622each include an arm 1624 and include a range of motion 1626. The arms1624 of the supplemental detector units 1622 may be extended orretracted (or otherwise articulated) to move the supplemental detectorunits 1622 radially toward or away from a bore 1602 of the imagingsystem 1600. As seen in FIG. 16 , the arms 1614 of the primary detectorunits 1612 are longer than the arms 1624 of the supplemental detectorunits 1622. Accordingly, the range of motion 1616 of the primarydetector units 1612 is greater than the range of motion 1626 of thesupplemental detector units, and the primary detector units 1612 areconfigured to advance further radially inwardly than the supplementaldetector units 1622. Utilizing supplemental detector units with a lowerrange of motion 1626 in various embodiments lowers costs as well asavoids potential collisions of supplemental detector units with primarydetector units if both are advanced too far radially inward. In someembodiments, the supplemental detector units 1622 may be fixed inposition, or have no range of motion radially, to further reduce costs.Additionally, or alternatively, the supplemental detector units may beremovable, and/or may be added only along a portion of the periphery ofthe bore 1602 (e.g., only along the upper half of the bore 1602) tofurther save space and/or cost.

Accordingly, in various embodiments, additional detector arms may beadded to an imaging system. The additional detector arms may beretracted, withdrawn, or otherwise positioned in a gantry between gapsof arms of primary detector units. For example, the additional detectorarms may be used with obese patients or otherwise larger than normalobjects to be imaged, and may have a limited radial motion. Shorteracquisition time and/or higher image quality may be obtained via theadditional detector arms. In addition to FIG. 16 , FIG. 18 provides anexample of an imaging system with additional or supplemental arms. FIG.18 provides a schematic view of an imaging system 1800.

As seen in FIG. 18 , the system 1800 includes primary arms (or mainarms) 1810, and supplemental arms (or additional arms) 1820. Outlinescorresponding to three different sizes of objects are shown in FIG. 18—a smallest object 1802, a nominal object 1804, and a largest object1806. The largest object 1806, for example, may correspond to an obesepatient. The smallest object 1802, for example, may correspond to aninfant, or, as another example, to a portion of an adult patient, suchas a brain or limb.

In the illustrated embodiment, the main arms 1810 have an extended orfull range of radial motion, while the supplemental arms 1820 have areduced range of radial motion or no radial motion at all. For example,the main arms 1810 may be radially extendable to reach the smallestobject 1802, while the supplemental arms may only be radially extendableto reach at or near the largest object 1806. As seen in FIG. 18 , toimage the smallest object 1802, every other main arm 1810 may beadvanced to the outline corresponding to the smallest object 1802, whilethe remaining main arms remain at the outline corresponding to thenominal object 1804, and the supplemental arms remain at the outlinecorresponding to the largest object 1806 (or may be removed from thesystem 1800). To image the nominal object 1804, all of the main arms1810 may be positioned at the outline corresponding to the nominalobject 1804, the supplemental arms remain at the outline correspondingto the largest object 1806 (or may be removed from the system 1800). Toimage the largest object 1806, the main arms and the supplemental armsmay be positioned at the outline corresponding to the largest object1806.

FIG. 17 provides a flowchart of a method 1700 for controlling detectorheads of a multi-head imaging system in accordance with variousembodiments. The method 1700 (or aspects thereof), for example, mayemploy or be performed by structures or aspects of various embodiments(e.g., systems and/or methods and/or process flows) discussed herein. Invarious embodiments, certain steps may be omitted or added, certainsteps may be combined, certain steps may be performed concurrently,certain steps may be split into multiple steps, certain steps may beperformed in a different order, or certain steps or series of steps maybe re-performed in an iterative fashion. In various embodiments,portions, aspects, and/or variations of the method 1700 may be able tobe used as one or more algorithms to direct hardware (e.g., one or moreaspects of the processing unit 120) to perform one or more operationsdescribed herein.

At 1702, an object to be imaged is positioned. The object, for example,may be a human patient (or portion thereof). In the depicted embodiment,the object is positioned within the bore of a gantry about whichmultiple detector units are positioned. Each detector unit is configuredto pivot or sweep with respect to the object being imaged, such that thefield of view of each detector unit is adjusted with respect to theobject as the detector unit is swept. In various embodiments, thedetector units may also rotate with the gantry, and/or be configured tobe moved radially toward or away from the center of the bore.

At 1704, plural angular positions are determined. In the illustratedexample, angular positions for each detector unit are determined along acorresponding sweep range for the given detector unit. The angularpositions, for example, may be determined by using photon counts from aninitial portion of a scan to determine boundaries or transitions (e.g.,between air and soft tissue, between soft tissue and a volume ofinterest). The initial portion of the scan to acquire the initialimaging information may be performed after positioning the object in thegantry, with the initial imaging information used to determine theangular positions (which in turn are used to determine scan parametersfor use in acquiring additional imaging information to be used toreconstruct a diagnostic image). It may be noted that in variousembodiments the initial imaging information is not used to reconstructan image before being used to determine the scan parameters as discussedherein. In some embodiments, four angular positions are determined: afirst angular position corresponding to a transition from air to softtissue in the field of view of the detector unit, a second angularposition corresponding to a transition from soft tissue surrounding avolume of interest to the volume of interest (e.g., one or moreparticular organs), a third angular position corresponding to atransition from the field of interest to soft tissue, and a fourthangular position corresponding to a transition from soft tissue to air.

At 1706, a representation (e.g., a plot) is generated for each angularposition for each detector unit position. At 1708, a model is generated(e.g., an angular positional curve is generated for each angularposition using a plot generated at 1706). For an example of such a plotand angular positional curves, see FIG. 11 and related discussion.

At 1710, scan parameters are determined. The scan parameters are for usein performing a diagnostic scan of the object being imaged, and aredetermined using the model (e.g., angular positional curves) generatedat 1708. Examples of scan parameters include, without limitation, sweeprange, sweep speed, radial position, number of detector units to beused, and gantry rotational position. In some embodiments, scanparameters may be determined for a detector unit position that was notused to acquire initial imaging information for use in determiningangular positions. For example, a detector unit may be idle during aninitial imaging information acquisition but used for a subsequentdiagnostic imaging acquisition. For instance, a first group of detectorsat a radially inward position may be used to acquire initial imaginginformation for determining scan parameters for both the first group ofdetectors as well as a second group of detectors that are at a radiallyoutward position during the initial acquisition, but are subsequentlymoved to the radially inward position for at least a portion of adiagnostic imaging acquisition.

As another example, scan parameters may be determined for at least oneadditional detector unit position corresponding to a rotation of thegantry. For instance, the at least one additional detector unit positionmay include a first additional detector unit position that is interposedbetween a first detector unit position of a first detector unit and asecond detector unit position of a second detector unit, with at leastone angular position for the first additional detector unit determinedusing the angular positional curve.

At 1712, imaging information is acquired using the determined scanparameters. For example, each detector unit may be used to acquireimaging information using a sweep range and one or more sweep speedsalong the range determined at 1710. For example, in various embodimentswhere four angular positions are determined as discussed in the exampledescribed in connection with step 1704, each detector unit may be sweptat a first, faster rate between the first angular position and thesecond angular position, swept at a second, slower rate between thesecond angular position and the third angular position, and swept at thefirst rate between the third angular position and fourth angularposition. Accordingly, more time is spent relatively over the volume ofinterest than over soft tissue outside of the volume of interest,providing more efficient imaging by acquiring relatively moreinformation of the volume of interest than would be acquired using asingle, constant sweep rate between the first and fourth angularpositions. It may be noted that, additionally or alternatively, imaginginformation may be acquired using one or more aspects of other methodsdiscussed herein, such as method 1300 and/or method 1500.

At 1714, an image is reconstructed using the imaging informationacquired at 1712. In some embodiments, initial imaging information usedto determine the angular positions may also be used in conjunction withthe imaging information acquire at 1712.

It should be noted that the particular arrangement of components (e.g.,the number, types, placement, or the like) of the illustratedembodiments may be modified in various alternate embodiments, and/or oneor more aspects of illustrated embodiments may be combined with one ormore aspects of other illustrated embodiments. For example, in variousembodiments, different numbers of a given module or unit may beemployed, a different type or types of a given module or unit may beemployed, a number of modules or units (or aspects thereof) may becombined, a given module or unit may be divided into plural modules (orsub-modules) or units (or sub-units), one or more aspects of one or moremodules may be shared between modules, a given module or unit may beadded, or a given module or unit may be omitted.

As used herein, a structure, limitation, or element that is “configuredto” perform a task or operation is particularly structurally formed,constructed, or adapted in a manner corresponding to the task oroperation. For purposes of clarity and the avoidance of doubt, an objectthat is merely capable of being modified to perform the task oroperation is not “configured to” perform the task or operation as usedherein. Instead, the use of “configured to” as used herein denotesstructural adaptations or characteristics, and denotes structuralrequirements of any structure, limitation, or element that is describedas being “configured to” perform the task or operation. For example, aprocessing unit, processor, or computer that is “configured to” performa task or operation may be understood as being particularly structuredto perform the task or operation (e.g., having one or more programs orinstructions stored thereon or used in conjunction therewith tailored orintended to perform the task or operation, and/or having an arrangementof processing circuitry tailored or intended to perform the task oroperation). For the purposes of clarity and the avoidance of doubt, ageneral purpose computer (which may become “configured to” perform thetask or operation if appropriately programmed) is not “configured to”perform a task or operation unless or until specifically programmed orstructurally modified to perform the task or operation.

As used herein, the term “computer,” “processor,” or “module” mayinclude any processor-based or microprocessor-based system includingsystems using microcontrollers, reduced instruction set computers(RISC), application specific integrated circuits (ASICs), logiccircuits, and any other circuit or processor capable of executing thefunctions described herein. The above examples are exemplary only, andare thus not intended to limit in any way the definition and/or meaningof the term “computer,” “processor,” or “module.”

The computer or processor executes a set of instructions that are storedin one or more storage elements, in order to process input data. Thestorage elements may also store data or other information as desired orneeded. The storage element may be in the form of an information sourceor a physical memory element within a processing machine.

The set of instructions may include various commands that instruct thecomputer or processor as a processing machine to perform specificoperations such as the methods and processes of the various embodiments.The set of instructions may be in the form of a software program. Thesoftware may be in various forms such as system software or applicationsoftware. Further, the software may be in the form of a collection ofseparate programs or modules, a program module within a larger programor a portion of a program module. The software also may include modularprogramming in the form of object-oriented programming. The processingof input data by the processing machine may be in response to operatorcommands, or in response to results of previous processing, or inresponse to a request made by another processing machine.

As used herein, the terms “software” and “firmware” may include anycomputer program stored in memory for execution by a computer, includingRAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatileRAM (NVRAM) memory. The above memory types are exemplary only, and arethus not limiting as to the types of memory usable for storage of acomputer program.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the variousembodiments without departing from their scope. While the dimensions andtypes of materials described herein are intended to define theparameters of the various embodiments, the embodiments are by no meanslimiting and are exemplary embodiments. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the various embodiments should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

In the appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects. Further, thelimitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. § 112(f), unless and until such claim limitations expresslyuse the phrase “means for” followed by a statement of function void offurther structure.

This written description uses examples to disclose the variousembodiments, including the best mode, and also to enable any personskilled in the art to practice the various embodiments, including makingand using any devices or systems and performing any incorporatedmethods. The patentable scope of the various embodiments is defined bythe claims, and may include other examples that occur to those skilledin the art. Such other examples are intended to be within the scope ofthe claims if the examples have structural elements that do not differfrom the literal language of the claims, or if the examples includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

What is claimed is:
 1. A method for use with a nuclear medicine (NM)multi-head imaging system comprising a plurality of detector unitsdistributed about a gantry, where each of the plurality of detectorunits is configured to pivot to define a corresponding sweep range, themethod comprising: determining plural angular positions along thecorresponding sweep range for each of the plurality of detector units;identifying a detector unit position based on a location of thecorresponding detector unit with respect to a bore of the gantry;generating a representation of the plural angular positions correlatedto detector unit position for each of the plurality of detector units;generating a model based on the plural angular positions using therepresentation, wherein the model includes, for each angular position,an angular positional curve comprising points corresponding to theangular position of each detector unit position of the plurality ofdetector units, wherein the angular positional curve for each angularposition includes points of corresponding detector unit positions forthat particular angular position, whereby each angular positional curveincludes points of multiple detector unit positions of the plurality ofdetector units for a respective angular position; determining scanparameters to be used to image an object using the model; acquiringimaging information using the determined scan parameters; reconstructingan image using the imaging information; and displaying the image on adisplay.
 2. The method of claim 1, further comprising determiningadditional scan parameters for at least one additional detector unitposition corresponding to a rotation of the gantry.
 3. The method ofclaim 2, wherein the at least one additional detector unit positionincludes a first additional detector unit position that is interposedbetween a first detector unit position of a first detector unit and asecond detector unit position of a second detector unit, and wherein theangular position for the first additional detector unit position isdetermined using the angular positional curve.
 4. The method of claim 1,wherein acquiring the imaging information comprises: sweeping eachdetector unit at a first rate between a first angular position and asecond angular position; sweeping each detector unit at a second ratebetween the second angular position and a third angular position; andsweeping each detector unit at a third rate between the third angularposition and a fourth angular position, wherein both the first rate andthe third rate are faster than the second rate.
 5. The method of claim4, wherein the second angular position is associated with a firstboundary of a volume of interest and the third angular position isassociated with a second boundary of the volume of interest.
 6. Themethod of claim 4, wherein the first rate is the same as the third rate.7. The method of claim 1, further comprising: advancing a first group ofdetector units to a first, radially inward position while leaving asecond group of detector units at a second, radially outward position;acquiring first imaging information with the first group of detectorunits at the first, radially inward position; retracting the first groupof detector units to the second, radially outward position; advancingthe second group of detector units to the first, radially inwardposition; and acquiring additional imaging information with the secondgroup of detector units at the first, radially inward position.
 8. Themethod of claim 1, further comprising: determining a regularly shapedfootprint that surrounds an irregular shape of the object to be imaged;advancing at least some of the plurality of detector units to theregularly shaped footprint; and acquiring imaging information with theat least some of the detector units positioned at the regularly shapedfootprint.
 9. The method of claim 1, wherein the plural angularpositions for each detector unit include a first angular positioncorresponding to a first boundary between air and tissue, a secondangular position corresponding to a first boundary between tissue and avolume of interest, a third angular position corresponding to a secondboundary between the volume of interest and tissue, and a fourth angularposition corresponding to a second boundary between tissue and air. 10.The method of claim 9, wherein acquiring the imaging informationcomprises: sweeping each detector unit at a first rate between the firstangular position and the second angular position; sweeping each detectorunit at a second rate between the second angular position and the thirdangular position, wherein the second rate is slower than the first rate;and sweeping each detector unit at the first rate between the thirdangular position and the fourth angular position.
 11. The method ofclaim 1, wherein the plural angular positions correspond to boundariesof at least one of the object or a volume of interest.
 12. The method ofclaim 11, wherein the plural angular positions are identified based ondata acquired during one or more preliminary sweeps with each of theplurality of detector units.
 13. A method for use with a nuclearmedicine (NM) multi-head imaging system comprising a plurality ofdetector units distributed about a gantry, where each of the pluralityof detector units is configured to pivot to define a corresponding sweeprange, the method comprising: determining plural angular positions alongthe corresponding sweep range for each of the plurality of detectorunits; identifying a detector unit position based on a location of thecorresponding detector unit with respect to a bore of the gantry;generating a representation of the plural angular positions correlatedto detector unit position for each of the plurality of detector units,wherein the representation correlates detector unit position along afirst axis and points corresponding to each of the plural angularpositions for each detector unit position of the plurality of detectorunits along a second axis perpendicular to the first axis; generating amodel based on the plural angular positions using the representation,wherein the model includes, for each angular position, an angularpositional curve comprising points corresponding to the angular positionof each detector unit position of the plurality of detector units,wherein the angular positional curve for each angular position includespoints of corresponding detector unit positions for that particularangular position, whereby each angular positional curve includes pointsof multiple detector unit positions of the plurality of detector unitsfor a respective angular position; determining scan parameters to beused to image an object using the model; acquiring imaging informationusing the determined scan parameters; reconstructing an image using theimaging information; and displaying the image on a display.
 14. Anon-transitory computer readable storage medium including instructionsthat, when executed, cause one or more processors to perform thefollowing: determine plural angular positions along a correspondingsweep range for each of a plurality of detector units of a nuclearmedicine (NM) multi-head imaging system, where each of the plurality ofdetector units is configured to pivot to define the corresponding sweeprange; identify a detector unit position based on a location of thecorresponding detector unit with respect to a bore of the NM multi-headimaging system; generate a representation of the plural angularpositions correlated to detector unit position for each of the pluralityof detector units, wherein the representation correlates detector unitposition along a first axis and points corresponding to each of theplural angular positions for each detector unit position of theplurality of detector units along a second axis perpendicular to thefirst axis; generate a model based on the plural angular positions usingthe representation, wherein the model includes, for each angularposition, an angular positional curve comprising points corresponding tothe angular position of each detector unit position of the plurality ofdetector units, wherein the angular positional curve for each angularposition includes points of corresponding detector unit positions forthat particular angular position, whereby each angular positional curveincludes points of multiple detector unit positions of the plurality ofdetector units for a respective angular position; determine scanparameters to be used to image an object using the model; acquireimaging information using the determined scan parameters; reconstruct animage using the imaging information; and display the image on a display.15. The non-transitory computer readable storage medium of claim 14,wherein the plural angular positions correspond to boundaries of theobject.
 16. The non-transitory computer readable storage medium of claim14, wherein the instructions, when executed, further cause the one ormore processors to: sweep each detector unit at a first rate between afirst angular position and a second angular position; sweep eachdetector unit at a second rate between the second angular position and athird angular position, wherein the first rate is faster than the secondrate; and sweep each detector unit at the first rate between the thirdangular position and a fourth angular position.
 17. The non-transitorycomputer readable storage medium of claim 14, wherein, when executed,further cause the one or more processors to identify the plural angularpositions based on data acquired during one or more preliminary sweepswith each of the plurality of detector units.